Gyroscope, methods of forming and operating the same

ABSTRACT

Various embodiments may provide a gyroscope. The gyroscope may include a piezoelectric substrate, an excitation transducer configured to generate a surface acoustic wave, and a sensing transducer configured to receive the surface acoustic wave generated by the excitation transducer. The gyroscope may additionally include a mass dot array between the excitation transducer and the sensing transducer, the mass dot array configured to generate a stress on the piezoelectric substrate based on a rotation of said gyroscope upon the surface acoustic wave passing through the mass dot array. The gyroscope may also include a light source, and an optical detector configured to receive one or more light beams generated by the light source to determine the rotation of the gyroscope based on a property of the one or more light beams. The property of the one or more light beams may be variable based on the stress on the piezoelectric substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority of Singapore applicationNo. 1020170691OR filed on Aug. 24, 2017, the contents of it being herebyincorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

Various aspects of this disclosure may relate to a gyroscope. Variousaspects of this disclosure may relate to a method of forming agyroscope. Various aspects of this disclosure may relate to a method ofoperating a gyroscope.

BACKGROUND

In recent years, the segment of microelectromechanical systems (MEMS)Coriolis gyroscopes is one of the fastest growing segments in the sensormarket, compared with optic and ring laser gyroscopes. This may be dueto the small size, promising performance, and low cost of the MEMSCoriolis gyroscopes. Two of the most important parameters for MEMSgyroscopes are resolution and anti-vibration or shock capability.

Mechanical vibrations in gyroscopes can create short term output errorsand degrade performance. Such output errors have been observed in manydevices, and the errors may be categorized as either false output orsensitivity change. The measure of the angular rate of a gyroscopeshould not be corrupted by linear acceleration, vibration, or shock. Ahigh rejection of environmental noise may be required for the reliableoperation of such devices.

FIG. 1 illustrates angular accelerations on a printed circuit boardcaused by vibrations.

SUMMARY

Various embodiments may provide a gyroscope. The gyroscope may include apiezoelectric substrate. The gyroscope may also include an excitationtransducer over the piezoelectric substrate, the excitation transducerconfigured to generate a surface acoustic wave. The gyroscope mayfurther include a sensing transducer over the piezoelectric substrate,the sensing transducer configured to receive the surface acoustic wavegenerated by the excitation transducer. The gyroscope may additionallyinclude a mass dot array over the piezoelectric substrate and betweenthe excitation transducer and the sensing transducer, the mass dot arrayconfigured to generate a stress on the piezoelectric substrate based ona rotation of said gyroscope upon the surface acoustic wave passingthrough the mass dot array. The gyroscope may also include a lightsource. The gyroscope may further include an optical detector configuredto receive one or more light beams generated by the light source todetermine the rotation of the gyroscope based on a property of the oneor more light beams. The property of the one or more light beams may bevariable based on the stress on the piezoelectric substrate.

Various embodiments may provide a method of forming a gyroscope. Themethod may include forming an excitation transducer over or on apiezoelectric substrate, the excitation transducer configured togenerate a surface acoustic wave. The method may also include forming asensing transducer over or on the piezoelectric substrate, the sensingtransducer configured to receive the surface acoustic wave generated bythe excitation transducer. The method may additionally include forming amass dot array over or on the piezoelectric substrate and between theexcitation transducer and the sensing transducer, the mass dot arrayconfigured to generate a stress on the piezoelectric substrate based ona rotation of said gyroscope upon the surface acoustic wave passingthrough the mass dot array. The method may also include coupling anoptical detector to a light source. The optical detector may beconfigured to receive one or more light beams generated by the lightsource to determine the rotation of the gyroscope based on a property ofthe one or more light beams. The property of the one or more light beamsmay be variable or changeable based on the stress on the piezoelectricsubstrate.

Various embodiments may provide a method of operating the gyroscope. Themethod may include using an excitation transducer, the excitationtransducer over a piezoelectric transducer, to generate a surfaceacoustic wave so that the surface acoustic wave is received by a sensingtransducer over the piezoelectric substrate. The surface acoustic wavemay pass through a mass dot array, the mass dot array between theexcitation transducer and the sensing transducer and over thepiezoelectric substrate. The method may further include rotating thegyroscope so that the array generates a stress on the piezoelectricsubstrate based on said rotation of the gyroscope upon the surfaceacoustic wave passing through the mass dot array. The method may alsoinclude determining the rotation of the gyroscope based on a property ofone or more light beams received by an optical detector over thepiezoelectric substrate, the optical detector optically coupled to alight source over the piezoelectric substrate. The property of the oneor more light beams may be variable or changeable based on the stress onthe piezoelectric substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the detaileddescription when considered in conjunction with the non-limitingexamples and the accompanying drawings, in which:

FIG. 1 illustrates angular accelerations on a printed circuit boardcaused by vibrations.

FIG. 2 shows a general illustration of the gyroscope according tovarious embodiments.

FIG. 3 shows a general illustration of a method of forming the gyroscopeaccording to various embodiments.

FIG. 4 shows a general illustration of a method of operating thegyroscope according to various embodiments.

FIG. 5A shows a schematic of a gyroscope according to variousembodiments.

FIG. 5B shows a diagram block of the gyroscope according to variousembodiments.

FIG. 5C is a schematic illustrate the different signals generated by thegyroscope according to various embodiments.

FIG. 5D is a schematic illustrating the Coriolis force generated by aparticle according to various embodiments.

FIG. 6 shows a schematic of a gyroscope 600 according to various otherembodiments.

FIG. 7A is a plot of depth (in ×10⁻⁵ metres or m) as a function of (in×10⁻⁵ in metres or m) showing the simulated standing mode shape of thegyroscope according to various embodiments.

FIG. 7B is a plot of impedance (in ohms) as a function of frequency (inhertz or Hz) showing the simulated frequency responses of the surfaceacoustic wave SAW resonators with different interdigitated transducer(IDT) finger space designs.

FIG. 8A is a plot of vertical direction (in micrometres or μm) as afunction of horizontal direction (in micrometres or μm) showing thesimulated optical mode in a waveguide according to various embodiments.

FIG. 8B is a plot of impedance (in ohms) as a function of stress on thephotonic waveguide (in mega Pascals or MPa) showing the simulated effectof stress on optical property of the waveguide according to variousembodiments.

FIG. 8C is a plot of the optical output (measured in volts or V) as afunction of the input angular rate (in degrees per second or deg/sec)illustrating the variation of the optical output of the gyroscopeaccording to various embodiments due to the applied input angular rate.

FIG. 9A shows a simulated stress distribution of the gyroscope accordingto various embodiments as a result of a 100, 000 g acceleration alongthe x-axis.

FIG. 9B shows a simulated stress distribution of the gyroscope accordingto various embodiments as a result of a 100, 000 g acceleration alongthe y-axis.

FIG. 9C shows a simulated stress distribution of the gyroscope accordingto various embodiments as a result of a 100, 000 g acceleration alongthe z-axis.

FIG. 10A shows the scanning electron microscope (SEM) image of thefabricated opto-mechanical gyroscope according to various embodiments.

FIG. 10B shows the scanning electron microscope (SEM) image of theresonator of the fabricated gyroscope according to various embodiments.

FIG. 10C shows the scanning electron microscope (SEM) image of thereflector part of the resonator of the gyroscope according to variousembodiments.

FIG. 10D is a schematic illustrating the designed surface acoustic wave(SAW) resonator according to various embodiments.

FIG. 10E shows the scanning electron microscope (SEM) image of awaveguide of the gyroscope according to various embodiments.

FIG. 10F shows the scanning electron microscope (SEM) image of awaveguide and the mass dot array of the gyroscope according to variousembodiments.

FIG. 11A is a plot of magnitude (in decibels or dB) as a function offrequency (in gigahertz or GHz) showing the measured magnitudetransmission response of the surface acoustic resonator of the gyroscopeaccording to various embodiments.

FIG. 11B is a plot of phase (in degrees or deg) as a function offrequency (in gigahertz or GHz) showing the measured phase transmissionresponse of the surface acoustic resonator of the gyroscope according tovarious embodiments.

FIG. 12A is a plot of power (in decibels (dB) with reference to onemilliwatt (mW) or dBm) as a function of frequency (in megahertz of MHz)showing the measured spectrum of the surface acoustic wave (SAW)oscillator of the gyroscope according to various embodiments.

FIG. 12B is a plot of power (in decibels (dB) with reference to carrieror dBc) as a function of frequency (in megahertz of MHz) showing themeasured phase noise of the surface acoustic wave (SAW) oscillator ofthe gyroscope according to various embodiments.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawingsthat show, by way of illustration, specific details and embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. Other embodiments may be utilized and structural, and logicalchanges may be made without departing from the scope of the invention.The various embodiments are not necessarily mutually exclusive, as someembodiments can be combined with one or more other embodiments to formnew embodiments.

Embodiments described in the context of one of the methods or gyroscopesare analogously valid for the other methods or gyroscopes. Similarly,embodiments described in the context of a method are analogously validfor a gyroscope, and vice versa.

Features that are described in the context of an embodiment maycorrespondingly be applicable to the same or similar features in theother embodiments. Features that are described in the context of anembodiment may correspondingly be applicable to the other embodiments,even if not explicitly described in these other embodiments.Furthermore, additions and/or combinations and/or alternatives asdescribed for a feature in the context of an embodiment maycorrespondingly be applicable to the same or similar feature in theother embodiments.

The word “over” used with regards to a deposited material formed “over”a side or surface, may be used herein to mean that the depositedmaterial may be formed “directly on”, e.g. in direct contact with, theimplied side or surface. The word “over” used with regards to adeposited material formed “over” a side or surface, may also be usedherein to mean that the deposited material may be formed “indirectly on”the implied side or surface with one or more additional layers beingarranged between the implied side or surface and the deposited material.In other words, a first layer “over” a second layer may refer to thefirst layer directly on the second layer, or that the first layer andthe second layer are separated by one or more intervening layers.

The gyroscope as described herein may be operable in variousorientations, and thus it should be understood that the terms “top”,“topmost”, “bottom”, “bottommost” etc., when used in the followingdescription are used for convenience and to aid understanding ofrelative positions or directions, and not intended to limit theorientation of the gyroscope.

In the context of various embodiments, the articles “a”, “an” and “the”as used with regard to a feature or element include a reference to oneor more of the features or elements.

In the context of various embodiments, the term “about” or“approximately” as applied to a numeric value encompasses the exactvalue and a reasonable variance.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

In order to reduce the bias drift of the MEMS gyroscope, the bias of thegyroscope should be reduced as much as possible. The two main sourcescausing the bias are: 1) electrical coupling between the driving signalsand the sensing signals, and 2) electrical direct motion coupling. Inorder to achieve high bias stability, we should reduce these electricalcouplings as much as possible.

Some groups proposed a surface acoustic wave (SAW) based gyroscope toachieve high stability to external vibrations and accelerations.Although the SAW based gyroscopes demonstrated the gyroscopic effect,the performances of these gyroscopes may still be far away fromexpectation. The driving and sensing interdigitated transducers (IDTs)still have large electrical coupling between each other.

Various embodiments may provide a gyroscope. FIG. 2 shows a generalillustration of the gyroscope 200 according to various embodiments. Thegyroscope 200 may include a piezoelectric substrate 202. The gyroscope200 may also include an excitation transducer 204 over or on thepiezoelectric substrate 202, the excitation transducer 204 configured togenerate a surface acoustic wave (SAW). The gyroscope 200 may furtherinclude a sensing transducer 206 over or on the piezoelectric substrate202, the sensing transducer 206 configured to receive the surfaceacoustic wave generated by the excitation transducer 204. The gyroscope200 may additionally include a mass dot array 208 over or on thepiezoelectric substrate 202, and between the excitation transducer 204and the sensing transducer 206, the mass dot array 208 configured togenerate a stress on the piezoelectric substrate 202 based on a rotationof said gyroscope 200 upon the surface acoustic wave passing through themass dot array 208. The gyroscope 200 may also include a light source210. The gyroscope 200 may further include an optical detector 212configured to receive one or more light beams generated by the lightsource 210 to determine the rotation of the gyroscope 200 based on aproperty of the one or more light beams. The property of the one or morelight beams may be variable or changeable based on the stress on thepiezoelectric substrate 202.

The gyroscope 200 may include a pair of transducers 204, 206 over asubstrate 202. Surface acoustic waves traveling between the pair oftransducers 204, 206 may pass through a mass dot array 208, and thevibrating mass dot array 208 may generate a stress distribution on thesubstrate 202 due to the Coriolis force acting on the mass dot array208, the Coriolis force produced as a result of the rotation of thegyroscope 200. The rotation of the gyroscope 200 may be determined byanalysing light passing from the light source 210 to the detector 212.

Various embodiments may address or mitigate the problems faced byconventional gyroscopes. Various embodiments may be robust as thegyroscope does not have suspended structures. Various embodiments mayhave high anti-shock ability, and may have high resistance to externalvibrations and/or accelerations. Various embodiments may have little orno cross-coupling between the driving loop (electrical signals drive thetransducers 208, 210), and the sense loop (optical signals passing fromthe light source 210 to the detector 212), thus resulting in highangular resolution. Various embodiments may have high bias stability.

In various embodiments, the mass dot array 208 may be configured togenerate a secondary wave, the secondary wave orthogonal to the surfaceacoustic wave passing through the mass dot array 208, based on aCoriolis force acting on the mass dot array 208 due to the rotation ofthe gyroscope 200.

The secondary wave may be a further surface acoustic wave (SAW), and maybe referred to as a rotation induced SAW. The surface acoustic wavegenerated by the excitation transducer 204 may be a standing wave.

The Coriolis force may be an inertial force that acts on an object thatis in motion relative to a rotating reference frame.

The gyroscope 200 may be rotated about an axis. The axis along which thegyroscope 200 is rotated may be orthogonal to both the surface acousticwave (generated by the excitation transducer 204) and the secondary wave(generated by the mass dot array 208).

The mass dot array 208 may include a plurality of microstructures ornanostructures. For instance, the mass dot array 208 may include aplurality of microparticles or nanoparticles. The mass dot array 208 maybe a regular, periodic array. The mass dot array 208 may be on or overthe substrate 202. The mass dot array 208 may also be between theexcitation transducer 204 and the sensing transducer 206.

The size of each mass dot (or each microstructure or nanostructure) maybe dependent on the wavelength of the excited surface acoustic wave(SAW). Generally, the size of each mass dot (or each microstructure ornanostructure) may be a square of a length substantially equal to ¼ of awavelength of the SAW.

The piezoelectric substrate 202 may include a suitable piezoelectricmaterial e.g. lithium niobate (LiNiO₃), lithium tantalate (LiTaO₃),aluminum nitride (AlN), zinc oxide (ZnO), or gallium nitride (GaN).

The piezoelectric substrate 202 may be a piezoelectric film.

In various embodiments, the light source 210 and/or the detector 212 maybe on chip. The light source 210 and/or the detector 212 may be over oron the piezoelectric substrate 202.

In various other embodiments, the light source 210 and/or the detector212 may be off chip.

In various embodiments, the light source 210 may be a laser source.Correspondingly, the one or more light beams may be laser beam(s).

The excitation transducer 202 may be an interdigitated transducer (IDT).The excitation transducer 202 may be referred to as a firstinterdigitated electrode

The sensing transducer 204 may be an interdigitated transducer (IDT).The sensing transducer 204 may be referred to as a second interdigitatedelectrode.

The gyroscope 200 may include a sustaining circuit in electricalconnection with the excitation transducer 202 and the sensing transducer204. The sustaining circuit may be configured to receive a transduceroutput signal from the sensing transducer 204 and may be furtherconfigured to provide a feedback signal to the excitation transducer 202based on the transducer output signal so that a standing wave ofconstant amplitude oscillating at a resonant frequency is generatedpassing through the mass dot array 208 between the excitation transducer202 and the sensing transducer 204. The sustaining circuit may be or mayinclude a sustaining amplifier. The sustaining circuit may be configuredto generate an amplified transducer output signal based on thetransducer output signal. The sustaining circuit may also be referred toas a sustain circuit.

The gyroscope 200 may further include a demodulator configured toreceive the transducer output signal from the sensing transducer 204, oran amplified transducer output signal from the sustaining circuit.

In various embodiments, the gyroscope 200 may include an amplifiercoupled to the optical detector 212 and the demodulator. The amplifiermay receive the optical output signal generated by the optical detector212, and may amplify the optical output signal optical output signalgenerated by the optical detector 212 before transmitting to thedemodulator. The amplifier may receive the optical output signalgenerated by the optical detector 212, and may generate the amplifiedoptical output signal based on the optical output signal.

The demodulator may be further configured to receive an optical outputsignal generated by the optical detector 212 based the one or more lightbeams, or an amplified optical output signal generated by an amplifiercoupled to the optical detector 212 and the demodulator.

The optical output signal (or amplified output signal) may be based onan oscillating frequency of the surface acoustic wave.

The demodulator may be configured to generate a demodulated outputsignal based on a demodulation of the optical output signal (oramplified output signal) by the transducer output signal (or amplifiedtransducer output signal). The rotation of the gyroscope 200 may bedetermined based on the demodulated output signal.

In various embodiments, the gyroscope 200 may include a first waveguidepositioned lateral to a first side of the mass dot array 208. Thegyroscope 200 may also include a second waveguide positioned lateral toa second side of the mass dot array opposite the first side (of the massdot array 208). In other words, the mass dot array 208 may be betweenthe first waveguide and the second waveguide. The first waveguide andthe second waveguide may be over or on the piezoelectric substrate 202.

The gyroscope 200 may also include a first Y-coupler configured tooptically couple the light source to a first end of the first waveguideand a first end of the second waveguide. The gyroscope 200 may alsoinclude a second Y-coupler configured to optically couple the opticaldetector to a second end of the first waveguide and a second end of thesecond waveguide. The first Y-coupler and/or the second Y-coupler may beover or on the piezoelectric substrate 202.

A Y-coupler may be an optical coupler that has three branches orwaveguides (joined or coupled together in a Y-shape). A light beamdirected into a first branch may be split and may pass out as separateoutput light beams from the second branch and the third branch. Further,a first light beam directed into the first branch and a second lightbeam directed into the second branch may be combined and pass out of thethird branch as a single output light beam.

The one or more light beams may travel from the light source 210 to thefirst Y-coupler, where the one or more light beams may be split up. Afirst light beam of the one or more light beams may be directed by thefirst Y-coupler to the first waveguide, and a second light beam of theone or more light beams may be directed by the first Y-coupler to thesecond waveguide. In such a scenario, the one or more light beams mayrefer to a plurality of light beams.

The stress generated by the mass dot array 208 on the piezoelectricsubstrate 202 may cause a tensile stress on the first waveguide and acompressive stress on the second waveguide. The first waveguide mayunder a change in an effective refractive index due to the tensilestress. The second waveguide may undergo a change in an effectiverefractive index (that is opposite to the change (in the effectiverefractive index) that is undergone by the first waveguide) due to thecompressive stress.

A first light beam of the one or more light beams traveling through thefirst waveguide may undergo a phase delay due to the tensile stress. Asecond light beam of the one or more light beams traveling through thesecond waveguide may undergo a phase forward due to the compressivestress.

The second Y-coupler may be coupled to the first waveguide and thesecond waveguide in such a manner that the second Y-coupler isconfigured to recombine the one or more light beams, which may travel tothe optical detector 212. For instance, the first light beam and thesecond light beam and recombine to form an interference light beam. Thelight beam that give rise to the first light beam and the second lightbeam, i.e. the light beam generated by the light source 210 beforesplitting at the first Y-coupler, may be referred to as the originallight beam.

The rotation of the gyroscope 202 may be determined based on a phasedifference between the first light beam and the second light beam, i.e.upon the light detector 212 receiving the interference light beam. Thephase difference between the first light beam and the second light beammay be determined by determining an intensity of an interference lightbeam generated by an interference of the first light beam and the secondlight beam. The intensity of the interference light beam received by thedetector may be different from the intensity of the original light beam.Accordingly, an intensity of the one or more light beams received by thelight detector 212 may be different from an intensity of the one or morelight beams generated by the light source 210. An output voltage may bedetermined from the gyroscope. The output voltage may be dependent onthe property of the one or more light beams, e.g. the change inintensity of the one or more light beams.

In various other embodiments, the gyroscope 200 may include a ringresonator that is optically coupled between the light source and theoptical detector. An input of the ring resonator may be opticallycoupled to the light source and an output of the ring resonator may beoptically coupled to the optical detector. The ring resonator may beover or on the substrate 202. The gyroscope 200 may have an inputwaveguide or an input waveguide section coupling the light source 210 tothe ring resonator. The gyroscope 200 may have an output waveguide or anoutput waveguide section coupling the ring resonator to the opticaldetector 212.

The stress on the piezoelectric substrate 202 may cause a change ineffective refractive index of the ring resonator, thus changing anintensity of the one or more light beams passing from the light sourceto the optical detector through the ring resonator.

In various embodiments, the property of the one or more light beams thatis variable may refer to an intensity of the one or more light beams.

The gyroscope 200 may be an integrated opto-mechanics gyroscope (IOMG).

Various embodiments may provide a method of forming a gyroscope. FIG. 3shows a general illustration of a method of forming the gyroscopeaccording to various embodiments. The method may include, in 302,forming an excitation transducer over or on a piezoelectric substrate,the excitation transducer configured to generate a surface acousticwave. The method may also include, in 304, forming a sensing transducerover or on the piezoelectric substrate, the sensing transducerconfigured to receive the surface acoustic wave generated by theexcitation transducer. The method may additionally include, in 306,forming a mass dot array over or on the piezoelectric substrate andbetween the excitation transducer and the sensing transducer, the massdot array configured to generate a stress on the piezoelectric substratebased on a rotation of said gyroscope upon the surface acoustic wavepassing through the mass dot array. The method may also include, in 308,coupling an optical detector to a light source. The optical detector maybe configured to receive one or more light beams generated by the lightsource to determine the rotation of the gyroscope based on a property ofthe one or more light beams. The property of the one or more light beamsmay be variable or changeable based on the stress on the piezoelectricsubstrate.

The method of forming the gyroscope may include forming the excitationtransducer, the sensing transducer, as well as the mass dot array overor on the piezoelectric substrate. The method may further includeoptically coupling a light source to an optical detector such that theone or more light beams generated by the light source and received bythe optical detector may be used to determine the rotation of thegyroscope based on a property of the one or more light beams.

For avoidance of doubt, the steps shown in FIG. 3 is not intended to bein sequence. For instance step 302 may occur before step 304, or mayoccur after or concurrently with step 304.

The method may further include electrically connecting a sustainingcircuit with the excitation transducer and the sensing transducer. Thesustaining circuit may be configured to receive a transducer outputsignal from the sensing transducer and may be further configured toprovide a feedback signal to the excitation transducer based on thetransducer output signal so that a standing wave of constant amplitudeoscillating at a resonant frequency is generated passing through themass dot array between the excitation transducer and the sensingtransducer.

The method may also include coupling a demodulator to the sensingtransducer via the sustaining circuit, and the optical detector via anamplifier. The demodulator may be configured to receive the transduceroutput signal from the sensing transducer, or an amplified transduceroutput signal from the sustaining circuit.

The method may include coupling an amplifier to the optical detector.The demodulator may be further configured to receive an optical outputsignal generated by the optical detector based the one or more lightbeams, or an amplified optical output signal generated by the amplifier.The demodulator may be configured to generate a demodulated outputsignal based on a demodulation of the optical output signal (or theamplified optical output signal) by the transducer output signal (or theamplified transducer output signal). The rotation of the gyroscope maybe determined based on the demodulated output signal.

In various embodiments, the method may include forming or positioning afirst waveguide lateral to a first side of the mass dot array. Themethod may also include forming or positioning a second waveguidepositioned lateral to a second side of the mass dot array opposite thefirst side. The method may additionally include forming or positioning afirst Y-coupler configured to optically couple the light source to afirst end of the first waveguide and a first end of the secondwaveguide. The method may also include forming or positioning a secondY-coupler configured to optically couple the optical detector to asecond end of the first waveguide and a second end of the secondwaveguide. The first waveguide, the second waveguide, the firstY-coupler, and/or the second Y-coupler may be formed or positioned on orover the piezoelectric substrate.

In various other embodiments, the method may include forming orpositioning a ring resonator that is optically coupled between the lightsource and the optical detector.

The method may include providing the piezoelectric substrate. The methodmay also include providing the light source. The method may also includeproviding the optical detector. The light source and/or the opticaldetector may be on-chip or off-chip.

In various embodiments, determining the rotation of the gyroscope mayrefer to determining the applied input angular rate on the gyroscope.

Various embodiments may provide a method of operating a gyroscope. FIG.4 shows a general illustration of a method of operating the gyroscopeaccording to various embodiments. The method may include, in 402, usingan excitation transducer, the excitation transducer over a piezoelectrictransducer, to generate a surface acoustic wave so that the surfaceacoustic wave is received by a sensing transducer over the piezoelectricsubstrate. The surface acoustic wave may pass through a mass dot array,the mass dot array between the excitation transducer and the sensingtransducer and over the piezoelectric substrate. The method may furtherinclude, in 404, rotating the gyroscope so that the array generates astress on the piezoelectric substrate based on said rotation of thegyroscope upon the surface acoustic wave passing through the mass dotarray. The method may also include, in 406, determining the rotation ofthe gyroscope based on a property of one or more light beams received byan optical detector over the piezoelectric substrate, the opticaldetector optically coupled to a light source over the piezoelectricsubstrate. The property of the one or more light beams may be variableor changeable based on the stress on the piezoelectric substrate.

The method of operating the gyroscope may include exciting thetransducer to generate the surface acoustic waves and rotating thegyroscope. The rotation of the gyroscope may then be determined based ona property one or more light beams travelling from the light source tothe optical detector as the property may be variable or changeable dueto stress on the piezoelectric substrate caused by the rotation of thegyroscope.

For avoidance of doubt, the steps shown in FIG. 4 is not intended to bein sequence.

In various embodiments, using an excitation transducer may includeapplying a voltage to the excitation transducer. A potential differencemay be applied between the excitation transducer and the sensingtransducer.

In various embodiments, the method may further include activating orturning on the light source.

In various embodiments, determining the rotation of the gyroscope mayinclude determining an output voltage of the gyroscope, the outputvoltage dependent on the property of the one or more light beams, e.g.the change in intensity of the one or more light beams

The mass dot array may be configured to generate a secondary wave, thesecondary wave orthogonal to the surface acoustic wave passing throughthe mass dot array, based on a Coriolis force acting on the mass dotarray due to the rotation of the gyroscope.

An axis along which the gyroscope is rotated may be orthogonal to boththe surface acoustic wave and the secondary wave.

The property of the one or more light beams may be an intensity of theone or more light beams, or a change in intensity of the one or morelight beams.

FIG. 5A shows a schematic of a gyroscope 500 according to variousembodiments. The gyroscope 500 may be an integrated opto-mechanicsgyroscope (IOMG). The gyroscope may include a SAW based mechanicalexcitation part, and a stress sensitive waveguide based optical sensingpart. The gyroscope 500 may be based on a surface acoustic wave (SAW)resonator, and a stress sensitive waveguide. The various components maybe made or formed on a piezoelectric substrate 502.

The SAW resonator may include an excitation inter-digital transducer(IDT) 504, the sensing IDT 506, and a resonant cavity between theexcitation IDT 502 and the sensing IDT 504. The excitation IDT 504 mayexcite a standing wave in the resonant cavity including a mass dot array508.

FIG. 5B shows a diagram block of the gyroscope 500 according to variousembodiments. The component portion of the gyroscope 500 is alreadyillustrated in FIG. 5A, and may include the SAW resonator (whichincludes IDTs 504, 506 and the resonant cavity), and the opticaldetector 512.

The sensing IDT 506 may be used to detect the output signals of the SAWresonator and feedback to a sustaining circuit 514 to make the SAWresonator oscillate at a resonant frequency. The sustaining circuit 514may maintain the SAW resonator oscillating with a constant amplitude.

The gyroscope 500 may further include a demodulator 516 coupled to thesustaining circuit 514, which may be a sustaining amplifier. Thegyroscope 500 may further include an amplifier 518 coupled to theoptical detector 512. An output signal of the optical detector 512 maybe amplified by the amplifier 518 before being transmitted to thedemodulator 516. The demodulator 516 may be coupled to the amplifier518.

The amplified output signal may be demodulated by the oscillationfrequency of the SAW resonator. The induced rotation rate may be deducedby the amplitude of the output voltage signal V_(out) from thedemodulator 516.

When the gyroscope 500 is rotated about the z-axis (see FIG. 5A), theCoriolis force acting on the vibrating mass dot array 508 may induce asecondary wave in the orthogonal direction of the standing wave. Thestanding wave may be parallel to the y-axis, while the second wave maybe parallel to the x-axis.

The induced secondary wave may cause periodic stress distribution on thesurface of the piezoelectric substrate 502. The stress distribution maybe detected using stress-sensitive optical sensing technology. FIG. 5Cis a schematic illustrate the different signals generated by thegyroscope 500 according to various embodiments. FIG. 5D is a schematicillustrating the Coriolis force generated by a particle according tovarious embodiments.

FIG. 5A illustrates a differential optical sensing design. The lasersource 510 may generate a light. The light may be coupled to an inputwaveguide 520, and may be split into two light beams by a Y-coupler 522coupled to the input waveguide 520. Each of the two light beams may passthrough a respective waveguide 524 a, 524 b. The SAW resonator may bebetween the two waveguides 524 a, 524 b. The two waveguides 524 a, 524 bmay be parallel to each other may be referred to as sensing waveguides.

Then, the two light beams may be coupled or combined together by anotherY-coupler 526, and may undergo interference along output waveguide 528before they enter into an optical detector 512. One waveguide 524 a(left side of the SAW resonator) may undergoes the tensile stress, andthe other waveguide 524 b on the other side (right side of the SAWresonator) may undergo compression stress. The tensile stress may causephase delay to the light beam traveling along waveguide 524 a, and thecompression stress may cause phase forward to the light beam travelingalong waveguide 524 b. The phase difference of the two light beams maybe deduced by measuring the intensity of the interference light based onthe two light beams. The output intensity (or change of output intensityfrom input intensity) of the light may indicate a phase difference ofthe two beams, which is caused by the Coriolis force induced stresses.Thus, the rotation that is applied may be deduced. The differentialapproach may reduce or eliminate common error signals caused by theexternal temperature changes or mechanical inferences.

FIG. 6 shows a schematic of a gyroscope 600 according to various otherembodiments. The gyroscope 600 may be a single-end stress sensingdesign. The gyroscope 600 may include a piezoelectric substrate 602, aswell as an excitation interdigitated transducer (IDT) 604 and a sensinginterdigitated transducer (IDT) 606 on the piezoelectric substrate 602.The gyroscope may further include a mass dot array 608 on thepiezoelectric substrate 602, the mass dot array 608 between theexcitation interdigitated transducer (IDT) 604 and the sensinginterdigitated transducer (IDT) 606.

The gyroscope 600 may further include a laser source 610, an opticaldetector 612, a bus waveguide 620, 628 (or referred to as a stresssensitive waveguide), and a ring resonator 624. The optical detector612, bus waveguide 620, 628, and ring resonator 624 may form the opticalreadout configuration. The bus waveguide 620, 628 may include an inputsection 620 configured to carry light from the laser source 610 to thering resonator 624, and an output section 628 configured to carry lightfrom the ring resonator 624 to the optical detector 612. In other words,the bus waveguide 620, 628 may be used to couple the light into and outfrom the ring resonator 624.

The mechanical stress induced by the Coriolis force may load onto thering resonator 624, which may then generate a small variation of theeffective refractive index. The small variation of the effectiverefractive index may affect the output light intensity of the ringresonator 624.

In various embodiments, the laser source 510, 610, and the detector 512,612 may be integrated on chip. In various other embodiments, the lasersource 510, 610, and the detector 512, 612 may be off chip. In otherwords, an off chip laser source and off chip detector may be used. Theoff chip laser source and the off chip detector may be integrated withthe remaining components on board level.

One feature of the gyroscope according to various embodiments is thatthe gyroscope has no suspended structure. Therefore, the gyroscope maybe highly robust, and may have excellent resilience to externalaccelerations and vibrations.

Another advantage of the gyroscope according to various embodiments isthat there may be no cross coupling between the drive loop and the senseloop. The drive loop may be based on the electrical signals, and thesensing loop may be based on the optical signals. There may be nocross-coupling between the drive loop and the sense loop, which resultsin a high angular resolution.

The gyroscope may include a piezoelectric substrate or a piezoelectricfilm (which can support a SAW along its surface), a SAW resonator, amass dot array, and an optical readout configuration (includingstress-sensitive waveguide(s)).

Finite elements method (FEM) simulation is done using COMSOL may help inthe design of the SAW resonator.

FIG. 7A is a plot of depth (in ×10⁻⁵ metres or m) as a function of (in×10⁻⁵ in metres or m) showing the simulated standing mode shape of thegyroscope according to various embodiments. FIG. 7A shows the surfaceacoustic wave mode shape.

FIG. 7B is a plot of impedance (in ohms) as a function of frequency (inhertz or Hz) showing the simulated frequency responses of the surfaceacoustic wave SAW resonators with different interdigitated transducer(IDT) finger space designs. The different curves in FIG. 7B representsIDTs with different spacings between the fingers and the reflectors. Thenumbers denoting the different lines are in micrometres.

FIG. 8A is a plot of vertical direction (in micrometres or μm) as afunction of horizontal direction (in micrometres or μm) showing thesimulated optical mode in a waveguide according to various embodiments.FIG. 8B is a plot of impedance (in ohms) as a function of stress on thephotonic waveguide (in mega Pascals or MPa) showing the simulated effectof stress on optical property of the waveguide according to variousembodiments. FIG. 8B illustrates the dependence of the effectiverefractive index (η_(eff)) of the waveguide due to the applied stress.The variation of the effective refractive index (η_(eff)) of thewaveguide due to the applied stress may be used to deduce the appliedinput angular rate on the gyroscope. FIG. 8C is a plot of the opticaloutput (measured in volts or V) as a function of the input angular rate(in degrees per second or deg/sec) illustrating the variation of theoptical output of the gyroscope according to various embodiments due tothe applied input angular rate.

The opto-mechanical gyroscope may have a high anti-shock ability and maybe immune to external vibrations. FIG. 9A shows a simulated stressdistribution of the gyroscope according to various embodiments as aresult of a 100, 000 g acceleration along the x-axis. FIG. 9B shows asimulated stress distribution of the gyroscope according to variousembodiments as a result of a 100, 000 g acceleration along the y-axis.FIG. 9C shows a simulated stress distribution of the gyroscope accordingto various embodiments as a result of a 100, 000 g acceleration alongthe z-axis. The simulation results indicate that the gyroscope mayendure 100, 000 g accelerations along the x-axis, y-axis, and z-axis.

The gyroscope may be fabricated based on aluminum nitride (AlN) on asilicon wafer. The MN may be a piezoelectric film. Surface acousticwaves may be excited in the AlN piezoelectric film.

FIG. 10A shows the scanning electron microscope (SEM) image of thefabricated opto-mechanical gyroscope according to various embodiments.FIG. 10B shows the scanning electron microscope (SEM) image of theresonator of the fabricated gyroscope according to various embodiments.FIG. 10C shows the scanning electron microscope (SEM) image of thereflector part of the resonator of the gyroscope according to variousembodiments. FIG. 10D is a schematic illustrating the designed surfaceacoustic wave (SAW) resonator according to various embodiments. FIG. 10Eshows the scanning electron microscope (SEM) image of a waveguide of thegyroscope according to various embodiments. FIG. 10F shows the scanningelectron microscope (SEM) image of a waveguide and the mass dot array ofthe gyroscope according to various embodiments.

The transmission response of the SAW resonator is characterized using anetwork analyzer. FIG. 11A is a plot of magnitude (in decibels or dB) asa function of frequency (in gigahertz or GHz) showing the measuredmagnitude transmission response of the surface acoustic resonator of thegyroscope according to various embodiments. FIG. 11B is a plot of phase(in degrees or deg) as a function of frequency (in gigahertz or GHz)showing the measured phase transmission response of the surface acousticresonator of the gyroscope according to various embodiments.

The SAW resonator may be connected to a sustain amplifier to achieve theoscillation. FIG. 12A is a plot of power (in decibels (dB) withreference to one milliwatt (mW) or dBm) as a function of frequency (inmegahertz of MHz) showing the measured spectrum of the surface acousticwave (SAW) oscillator of the gyroscope according to various embodiments.FIG. 12B is a plot of power (in decibels (dB) with reference to carrieror dBc) as a function of frequency (in megahertz of MHz) showing themeasured phase noise of the surface acoustic wave (SAW) oscillator ofthe gyroscope according to various embodiments. FIG. 12B shows themeasured phase noise of the SAW oscillator output at 4.4 GHz. Theoscillation power is −1.34 dBm. The measured phase noises are −87.22dBc/Hz, −116.75 dBc/Hz, −142.58 and −146.54 dBc/Hz with offsets of 10kHz, 100 kHz, 1 MHz and 10 MHz, respectively.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. The scope of the invention is thusindicated by the appended claims and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced.

1. A gyroscope comprising: a piezoelectric substrate; an excitationtransducer over the piezoelectric substrate, the excitation transducerconfigured to generate a surface acoustic wave; a sensing transducerover the piezoelectric substrate, the sensing transducer configured toreceive the surface acoustic wave generated by the excitationtransducer; a mass dot array over the piezoelectric substrate andbetween the excitation transducer and the sensing transducer, the massdot array configured to generate a stress on the piezoelectric substratebased on a rotation of said gyroscope upon the surface acoustic wavepassing through the mass dot array; a light source; and an opticaldetector optically coupled to the light source; wherein the opticaldetector is configured to receive one or more light beams generated bythe light source to determine the rotation of the gyroscope based on aproperty of the one or more light beams; and wherein the property of theone or more light beams is variable based on the stress on thepiezoelectric substrate.
 2. The gyroscope according to claim 1, whereinthe mass dot array is configured to generate a secondary wave, thesecondary wave orthogonal to the surface acoustic wave passing throughthe mass dot array, based on a Coriolis force acting on the mass dotarray due to the rotation of the gyroscope.
 3. The gyroscope accordingto claim 2, wherein an axis along which the gyroscope is rotated isorthogonal to both the surface acoustic wave and the secondary wave. 4.The gyroscope according to claim 1, wherein the mass dot array comprisesa plurality of microstructures or nano structures.
 5. The gyroscopeaccording to claim 1, further comprising: a sustaining circuit inelectrical connection with the excitation transducer and the sensingtransducer; wherein the sustaining circuit is configured to receive atransducer output signal from the sensing transducer and furtherconfigured to provide a feedback signal to the excitation transducerbased on the transducer output signal so that a standing wave ofconstant amplitude oscillating at a resonant frequency is generatedpassing through the mass dot array between the excitation transducer andthe sensing transducer.
 6. The gyroscope according to claim 5, furthercomprising: a demodulator configured to receive the transducer outputsignal from the sensing transducer, wherein the demodulator is furtherconfigured to receive an optical output signal generated by the opticaldetector based the one or more light beams; and wherein the demodulatoris configured to generate a demodulated output signal based on ademodulation of the optical output signal by the transducer outputsignal; wherein the rotation of the gyroscope is determined based on thedemodulated output signal.
 7. The gyroscope according to claim 1,further comprising: a first waveguide positioned lateral to a first sideof the mass dot array; a second waveguide positioned lateral to a secondside of the mass dot array opposite the first side; a first Y-couplerconfigured to optically couple the light source to a first end of thefirst waveguide and a first end of the second waveguide; a secondY-coupler configured to optically couple the optical detector to asecond end of the first waveguide and a second end of the secondwaveguide.
 8. The gyroscope according to claim 7, wherein the stressgenerated by the mass dot array on the piezoelectric substrate causes atensile stress on the first waveguide and a compressive stress on thesecond waveguide; wherein a first light beam of the one or more lightbeams traveling through the first waveguide undergoes a phase delay dueto the tensile stress; and wherein a second light beam of the one ormore light beams traveling through the second waveguide undergoes aphase forward due to the compressive stress.
 9. The gyroscope accordingto claim 8, wherein the rotation of the gyroscope is determined based ona phase difference between the first light beam and the second lightbeam.
 10. The gyroscope according to claim 9, wherein the phasedifference between the first light beam and the second light beam isdetermined by determining an intensity of an interference light beamgenerated by an interference of the first light beam and the secondlight beam.
 11. The gyroscope according to any claim 1, furthercomprising: a ring resonator that is optically coupled between the lightsource and the optical detector.
 12. The gyroscope according to claim11, wherein the stress on the piezoelectric substrate causes a change ineffective refractive index of the ring resonator, thus changing anintensity of the one or more light beams passing from the light sourceto the optical detector through the ring resonator.
 13. The gyroscopeaccording to claim 12, wherein the rotation of the gyroscope isdetermined by the change in the intensity.
 14. The gyroscope accordingto claim 1, wherein the excitation transducer comprises a firstinterdigitated electrode; and wherein the sensing transducer comprises asecond interdigitated electrode.
 15. The gyroscope according to claim 1,wherein the light source is a laser source.
 16. A method of forming agyroscope, the method comprising: forming an excitation transducer overa piezoelectric substrate, the excitation transducer configured togenerate a surface acoustic wave; forming a sensing transducer over thepiezoelectric substrate, the sensing transducer configured to receivethe surface acoustic wave generated by the excitation transducer;forming a mass dot array over the piezoelectric substrate and betweenthe excitation transducer and the sensing transducer, the mass dot arrayconfigured to generate a stress on the piezoelectric substrate based ona rotation of said gyroscope upon the surface acoustic wave passingthrough the mass dot array; and coupling an optical detector to a lightsource; wherein the optical detector is configured to receive one ormore light beams generated by the light source to determine the rotationof the gyroscope based on a property of the one or more light beams; andwherein the property of the one or more light beams is variable based onthe stress on the piezoelectric substrate.
 17. A method of operating agyroscope, the method comprising using an excitation transducer over apiezoelectric transducer to generate a surface acoustic wave so that thesurface acoustic wave is received by a sensing transducer over thepiezoelectric substrate, wherein the surface acoustic wave passesthrough a mass dot array, the mass dot array between the excitationtransducer and the sensing transducer and over the piezoelectricsubstrate; rotating the gyroscope so that the array generates a stresson the piezoelectric substrate based on said rotation of the gyroscopeupon the surface acoustic wave passing through the mass dot array; anddetermining the rotation of the gyroscope based on a property of one ormore light beams received by an optical detector over the piezoelectricsubstrate, the optical detector optically coupled to a light source overthe piezoelectric substrate; wherein the property of the one or morelight beams is variable based on the stress on the piezoelectricsubstrate.
 18. The method according to claim 17, wherein the mass dotarray is configured to generate a secondary wave, the secondary waveorthogonal to the surface acoustic wave passing through the mass dotarray, based on a Coriolis force acting on the mass dot array due to therotation of the gyroscope.
 19. The method according to claim 18, whereinan axis along which the gyroscope is rotated is orthogonal to both thesurface acoustic wave and the secondary wave.
 20. The method accordingto claim 17, wherein the property is an intensity of the one or morelight beams.